Distributed tunneling for VPN

ABSTRACT

A novel method of providing virtual private access to a software defined data center (SDDC) is provided. The SDDC uses distributed VPN tunneling to allow external access to application services hosted in the SDDC. The SDDC includes host machines for providing computing and networking resources and a VPN gateway for providing external access to those resources. The host machines that host the VMs running the applications that VPN clients are interested in connecting performs the VPN encryption and decryption. The VPN gateway does not perform any encryption and decryption operations. The packet structure is such that the VPN gateway can read the IP address of the VM without decrypting the packet.

CLAIM OF BENEFIT TO PRIOR APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/140,027, filed Apr. 27, 2016, now published asU.S. Patent Publication 2017/0034129. U.S. patent application Ser. No.15/140,027 claims the benefit of Indian Patent Application No.201641005073, filed Feb. 12, 2016. U.S. patent application Ser. No.15/140,027 is also a Continuation In Part application of U.S. patentapplication Ser. No. 14/815,074, filed Jul. 31, 2015, now issued as U.S.Pat. No. 10,044,502. Indian Patent Application No. 201641005073. U.S.patent application Ser. No. 14/815,074, now issued as U.S. Pat. No.10,044,502, and U.S. patent application Ser. No. 15/140,027, nowpublished as U.S. Patent Publication 2017/0034129 are incorporatedherein by reference.

BACKGROUND

When a user accesses application services hosted in a software defineddata center (SDDC) using a mobile device over a public network such asInternet, the data traffic needs to be secured end-to-end with the helpof a secure channel such as through virtual private network (VPN). Themobile device communicates with an application server running inside aVM hosted on a hypervisor within the enterprise's data center. Thegateway of the data center on the data path between the remote mobiledevice and the application server typically act as the VPN server. A VPNserver typically performs encryption and decryption for VPN channels toand from VMs within the data center. As VPN encryption and decryptionare time consuming operations, VPN server can become performancebottleneck.

SUMMARY

Some embodiments provide a SDDC that uses distributed VPN tunneling toallow external access to application services hosted in the SDDC. TheSDDC includes host machines for providing computing and networkingresources and a VPN gateway for providing external access to thoseresources. Some embodiments perform VPN operations in the host machinesthat host the VMs running the applications that VPN clients areinterested in connecting. In some embodiments, the VPN gateway does notperform any encryption and decryption operations. In some embodiments,the packet structure is such that the VPN gateway can read the IPaddress of the VM without decrypting the packet.

Some embodiments use Distributed Network Encryption (DNE) to establish ashared key for VPN encryption. DNE is a mechanism for distributedentities in a data center to share a key. The key management is donecentrally from an entity called DNE Key Manager, which communicates withDNE Agents in the hypervisors using a secure control channel. The keysare synced between the Agents, which can work then onwards withoutrequiring the DNE Key Manager to be online.

In some embodiments, when a packet is generated by an application at aVPN client, the VPN client encrypts the packet with VPN encryption keyand processes the packet into an IPSec packet with IPSec header. TheIPSec packet is then sent through the Internet to the VPN gateway of thedatacenter, with the content of the packet encrypted. The VPN gateway ofthe data center then tunnels the packet to its destination tunnelendpoint (a host machine) by encapsulating it (under overlay such asVXLAN). The host machine that receives the tunnel packet in turnde-capsulate the packet, decrypt the packet, and forward the decrypteddata to the destination VM/application.

In some embodiments, a VPN gateway does not perform VPN encryption ordecryption. When the VPN gateway receives an encrypted VPN packet overthe Internet, it identifies the destination tunnel endpoint (i.e.,destination host machine) and the destination VM without decrypting thepacket. In some embodiments, the VPN gateway uses information in the IPheader to identify destination host machine and destination VM, and theVPN client leaves the IP header unencrypted. In some embodiments, theVPN client encrypt the IP header along with the payload of the packet,but replicates certain portion or fields (e.g., destination IP) of theIP header in an unencrypted portion of the packet so the VPN gatewaywould be able to forward the packet to its destination in the datacenter.

The preceding Summary is intended to serve as a brief introduction tosome embodiments of the invention. It is not meant to be an introductionor overview of all inventive subject matter disclosed in this document.The Detailed Description that follows and the Drawings that are referredto in the Detailed Description will further describe the embodimentsdescribed in the Summary as well as other embodiments. Accordingly, tounderstand all the embodiments described by this document, a full reviewof the Summary, Detailed Description and the Drawings is needed.Moreover, the claimed subject matters are not to be limited by theillustrative details in the Summary, Detailed Description and theDrawings, but rather are to be defined by the appended claims, becausethe claimed subject matters can be embodied in other specific formswithout departing from the spirit of the subject matters.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. However, for purpose of explanation, several embodiments of theinvention are set forth in the following figures.

FIG. 1 illustrates a datacenter that provides VPN services to allowexternal access to its internal resources.

FIG. 2 illustrates a VPN connection between different sites in amulti-site environment.

FIG. 3 illustrates the distribution of VPN traffic among multiple edgenodes in and out of a datacenter.

FIG. 4 illustrates the distribution of VPN traffic among multiple edgenodes between datacenters.

FIG. 5 illustrates an edge node of a data center serving as VPN gatewayfor different VPN connections.

FIGS. 6a-b conceptually illustrate the distribution of VPN encryptionkeys from an edge to host machines through control plane.

FIG. 7 conceptually illustrates a process for creating and using a VPNsession.

FIG. 8 illustrates packet-processing operations that take place alongthe VPN connection data path when sending a packet from a VPN clientdevice to a VM operating in a host machine.

FIG. 9 illustrates the various stages of packet encapsulation andencryption in a distributed tunneling based VPN connection.

FIG. 10 conceptually illustrates processes for preparing a packet forVPN transmission.

FIG. 11 conceptually illustrates a process for forwarding packet at aVPN gateway of a data center.

FIG. 12 illustrates host machines in multi-site environment performingflow-specific VPN encryption and decryption.

FIG. 13 conceptually illustrate the distribution of VPN encryption keysfrom an edge to host machines through control plane.

FIG. 14 conceptually illustrates a process that is performed by a hostmachine in a datacenter that uses VPN to communicate with externalnetwork or devices.

FIG. 15 illustrates packet-processing operations that take place alongthe data path when sending a packet from one site to another site byusing VPN.

FIG. 16 illustrates using partial decryption of the VPN encrypted packetto identify the packet's rightful destination.

FIG. 17 conceptually illustrates a process for forwarding VPN encryptedpacket at an edge node.

FIG. 18 illustrates a computing device that serves as a host machine.

FIG. 19 conceptually illustrates an electronic system with which someembodiments of the invention are implemented.

DETAILED DESCRIPTION

In the following description, numerous details are set forth for thepurpose of explanation. However, one of ordinary skill in the art willrealize that the invention may be practiced without the use of thesespecific details. In other instances, well-known structures and devicesare shown in block diagram form in order not to obscure the descriptionof the invention with unnecessary detail.

Some embodiments provide a SDDC that uses distributed VPN tunneling toallow external access to application services hosted in the SDDC. TheSDDC includes host machines for providing computing and networkingresources and a VPN gateway for providing external access to thoseresources. Some embodiments perform VPN operations in the host machinesthat host the VMs running the applications that VPN clients areinterested in connecting. In some embodiments, the VPN gateway does notperform any encryption and decryption operations. In some embodiments,the packet structure is such that the VPN gateway can read the IPaddress of the VM without decrypting the packet.

I. Distributed VPN Tunneling

For some embodiments, FIG. 1 illustrates a datacenter 100 that providesVPN services to allow external access to its internal resources. Thedatacenter 100 is a SDDC that provides computing and/or networkingresources to tenants or clients. The computing and/or network resourcesof the SDDC are logically organized into logical networks for differenttenants, where the computing and networking resources are accessible orcontrollable as network nodes of these logical networks. In someembodiments, some of the computing and network resources of the SDDC areprovided by computing devices that serve as host machines for virtualmachines (VMs). These VMs in turn perform various operations, includingrunning applications for tenants of the datacenter. As illustrated, thedatacenter 100 includes host machines 111-113. The host machine 113 inparticular is hosting a VM that is running an application 123. Thedatacenter 100 also has an edge node 110 for providing edge services andfor interfacing the external world through the Internet 199. In someembodiments, a host machine in the datacenter 100 is operating a VM thatimplements the edge node 110. (Computing devices serving as hostmachines will be further described by reference to FIG. 18 below.)

Devices external to the datacenter 100 can access the resources of thedatacenter (e.g., by appearing as a node in a network of the datacenter100) by using the VPN service provided by the datacenter 100, where theedge 110 is serving as the VPN gateway (or VPN server) for thedatacenter 100. In the illustrated example, a device 105 external to thedatacenter 100 is operating an application 120. Such a device can be acomputer, a smart phone, other types of mobile devices, or any otherdevice capable of secure data communicating with the datacenter. Theapplication 120 is in VPN communication with the datacenter 100 over theInternet.

The VPN communication is provided by a VPN connection 195 establishedover the Internet between a VPN client 130 and the edge node 110. TheVPN connection 195 allows the application 120 to communicate with theapplication 123, even though the application 120 is running on a deviceexternal to the datacenter 100 while the application 123 is running on ahost machine internal to the datacenter 100. The VPN connection 195 is asecured, encrypted connection over the Internet 199. The encryptionprotects the data traffic over the Internet 199 when it travels betweenthe VPN client 130 and the edge 110.

In some embodiments, an edge node (such as 110) of the data centerserves as a VPN gateway/VPN server to allow external networks or devicesto connect into the SDDC via a tunneling mechanism over SSL/DTLS orIKE/IPSec. In some embodiments, the VPN server has a public IP addressfacing the Internet and a private IP address facing the datacenter. Insome embodiments, the VPN server in a SDDC is a software appliance(e.g., a VM running on a host machine) rather than a hardware networkappliance.

The encryption of the VPN connection 195 is based on a key 150 that isnegotiated by the edge 110 and the VPN client 130. In some embodiments,the edge negotiates such a key based on the security policies that isapplicable to the data traffic (e.g., based on the flow/L4 connection ofthe packets, or based on L2 segment/VNI of the packets). The VPN client130 uses this key 150 to encrypt and decrypt data to and from the VPNconnection 195 for the application 120. Likewise, the host machine 113uses the key 150 to encrypt and decrypt data to and from the VPNconnection 195 for the application 123. As illustrated, the application120 produces a packet 170. A crypto engine 160 in the VPN client 130encrypts the packet 170 into an encrypted packet 172 by using theencryption key 150. The encrypted packet 172 travels through theInternet to reach the edge 110 of the datacenter 100. The edge 110forwards the encrypted packet 172 to the host machine 113 by e.g.,routing and/or encapsulating the encrypted packet. The host machine 113has a crypto engine 165 that uses the encryption key 150 to decrypt therouted encrypted packet 172 into a decrypted packet 176 for the VM 143,which is running the application 123. In some embodiments, the cryptoengine 165 is a module or function in the virtualizationsoftware/hypervisor of the host machine.

It is worth emphasizing that the encryption and the decryption oftraffic across VPN connection is conducted near the true endpoint of theVPN traffic, rather than by the edge node that negotiated the encryptionkey of the VPN connection. In the example of FIG. 1, the true endpointof the VPN traffic across the VPN connection 195 are application 120 andthe application 123. The application 123 is running on the host machine113, and the encryption/decryption is handled at the host machine 113rather than at the edge node 110 (which negotiated the encryption key150). In some embodiments, the machines in the datacenter are operatingvirtualization software (or hypervisors) in order to operate virtualmachines, and the virtualization software running on a host machinehandles the encryption and the decryption of the VPN traffic for the VMsof the host machine. Having encryption/decryption handled by the hostmachines rather than by the edge has the advantage of freeing the edgenode from having to perform encryption and decryption for all VPNtraffic in and out of the datacenter. Performing end-to-end VPNencryption/decryption also provides higher level of security thanperforming encryption/decryption at the edge because the VPN packetsremain encrypted from the edge all the way to the host machine (and viceversa).

FIG. 1 illustrates a VPN connection that is established between adatacenter's edge node and a VPN client. In some embodiments, acomputing device that is running an application that requires VPN accessto a datacenter also operates the VPN client in order for theapplication to gain VPN access into the datacenter. In the example ofFIG. 1, the computing device 105 external to the datacenter 100 isoperating the VPN client 130 as well as the application 120 in order toestablish the VPN connection 195. In some embodiments, a physical deviceseparate from the computing device 105 provides the VPN clientfunctionality. In either instance, a computing device operating a VPNclient is referred to as a VPN client device in some embodiments.

In some embodiments, a datacenter is deployed across multiple sites inseparate physical locales, and these different sites are communicativelyinterlinked through the Internet. In some embodiments, each physicalsite is regarded as a datacenter and the different datacenters or sitesare interlinked through the Internet to provide a multi-siteenvironment. Some embodiments use VPN communications to conduct trafficsecurely between the different sites through the Internet. In someembodiments, each of the sites has an edge node interfacing theInternet, and the VPN connection between the different sites areencrypted by encryption keys negotiated between the edge nodes ofdifferent sites. The host machines in those sites in turn use thenegotiated keys to encrypt and/or decrypt the data for VPNcommunications.

FIG. 2 illustrates distributed VPN tunneling between different sites ina multi-site environment 200 (or multi-site datacenter). The multi-siteenvironment 200 includes two sites 201 and 202 (site A and site B). Thesite 201 has host machines 211-213 and an edge node 210 for interfacingthe Internet 199. The site 202 includes host machines 221-223 and anedge node 220 for interfacing the Internet 199. The edge nodes 210 and220 serve as the VPN gateways for their respective sites.

The host machine 212 of site A is running an application 241 and thehost machine 223 is running an application 242. The application 241 andthe application 242 communicates with each other through a VPNconnection 295 as the two applications 241 and 242 are running indifferent sites separated by the Internet 199. The VPN connection sendstraffic that are encrypted by a key 250, which is the VPN encryption keynegotiated between the edge 210 and the edge 220. Although the edgenodes 210 and 220 negotiated the key 250 for the VPN connection 295, thekey 250 is provided to the host machines 212 and 223 so those hostmachines can perform the encryption/decryption for the VPN connectionnear the endpoints of the traffic (i.e., the applications 241 and 242).

As illustrated, a VM 231 of the host machine 212 produces a packet 270(for the application 241). A crypto engine 261 in the host machine 212encrypts the packet 270 into an encrypted packet 272 by using theencryption key 250. The host machine 212 forwards the encrypted packet272 to the edge 210 of the site 201 by e.g., routing and/orencapsulating the packet. The edge 210 of site A in turn sends theencrypted packet 272 to the edge 220 of site B through the Internet (bye.g., using IPSec tunnel). The edge 220 forwards the encrypted packet272 to the host machine to the host machine 223 by e.g., routing and/orencapsulating the encrypted packet. The host machine 223 has a cryptoengine 262 that uses the encryption key 250 to decrypt the encryptedpacket 272 into a decrypted packet 276 for a VM 232, which is runningthe application 223.

By performing VPN encryption/decryption at the host machines rather thanat the edge, a datacenter or site is effectively implementing adistributed VPN system in which the tasks of implementing a VPNconnection is distributed to the host machines from the edge node. Insome embodiments, a site or datacenter has multiple edge nodes, and theVPN traffic to and from this site is further distributed among thedifferent edge nodes.

FIGS. 3a-b illustrates the distribution of VPN traffic among multipleedge nodes in and out of a site/datacenter. The figure illustrates adata center 301, which can be a site in a multi-site environment. Thedata center 301 has edge nodes 311 and 312 as well as host machines321-323. Both edge nodes 311 and 312 are serving as VPN gateways for thedata center 301. In some embodiments, traffic of one VPN connection canbe distributed across multiple VPN gateways.

FIG. 3a illustrates the two edge nodes 311 and 312 jointly serving oneVPN connection between a VPN client 313 and a host machine 322. Asillustrated, the host machine 322 is operating a VM 329 and the VPNclient is 313 is running an application 343. The packet traffic betweenthe VM 329 and the application 343 can flow through either the edge node311 or 312. Both the VPN client 313 and the host machine 322 use thesame key 350 to encrypt and decrypt traffic, while the edge nodes 311and 312 do not perform any encryption or decryption.

In some embodiments, different edge gateways can serve different VPNconnections. FIG. 3b illustrates the two edge nodes 311 and 312 servingtwo different VPN connections for two different VPN clients 314 and 315.As illustrated, there is a first VPN connection between the host machine322 and a VPN client 314 and a second VPN connection between the hostmachine 323 and a VPN client 315. The first VPN connection uses the edgenode 311 to conduct traffic between the application 344 and the VM 327,while the second VPN connection uses the edge node 312 to conducttraffic between the application 345 and the VM 328. These two VPNconnections use different keys 351 and 352 to encrypt and decrypttraffic. The host machine 322 and the VPN client 314 use the key 351 toperform the encryption and decryption of the VPN connection between theVM 327 and the App 344. The host machine 323 and the VPN client 315 usethe key 352 to perform the encryption and decryption of the VPNconnection between the VM 328 and the App 345.

FIG. 4 illustrates the distribution of VPN traffic among multiple edgenodes between multiple data centers. The figure illustrates a multi-siteenvironment 400 having sites 401 (site C) and 402 (site D). Site C hasedge nodes 411 and 412 as well as host machines 421-423. Site D has anedge node 413 and host machines 431-433. The edge node 413 is serving asthe VPN gateway for the site 402. Both edge nodes 411 and 412 areserving as VPN gateways for the site 401.

The host machine 422 of site C and the host machine 433 of site D are inVPN communication with each other for an application 429 running on thehost machine 422 and an application 439 running in the host machine 433.The encryption/decryption of the VPN traffic is performed by the hostmachines 422 and 433 and based on a key 450 that is negotiated betweenthe edge nodes 411, 412 and 413. The encrypted VPN traffic entering andleaving site D is only through the edge node 413, while the same trafficentering and leaving site C is distributed among the edge nodes 411 and412.

As illustrated, a VM 442 running on the host machine 422 of site Cgenerates packets 471 and 472 for the application 429. A crypto engine461 of the host machine 422 encrypts these two packets into encryptedpackets 481 and 482 using the encryption key 450. The encrypted packet481 exits site C through the edge 411 into the Internet while theencrypted packet 482 exits site C through the edge 412 into theInternet. Both the encrypted packet 481 and 482 reaches site D throughthe edge 413, which forwards the encrypted packet to the host machine433. The host machine 433 has a crypto engine 462 that uses the key 450to decrypt the packets 481 and 482 for a VM 443, which is running theapplication 439.

In some embodiments, each edge node is responsible for both negotiatingencryption keys as well as handling packet forwarding. In someembodiments, one set of edge nodes is responsible for handlingencryption key negotiation, while another set of edge nodes serves asVPN tunnel switch nodes at the perimeter for handling the mapping of theouter tunnel tags to the internal network hosts and for forwarding thepackets to the correct host for processing, apart from negotiating thekeys for the connection.

Some embodiments negotiate different encryption keys for different L4connections (also referred to as flows or transport sessions), and eachhost machines running an applications using one of those L4 connectionswould use the corresponding flow-specific key to perform encryption.Consequently, each host machine only need to perform VPNdecryption/encryption for the L4 connection/session that the hostmachine is running.

In some embodiments, one edge node can serve as the VPN gateway formultiple different VPN connections. FIG. 5 illustrates the edge node 110of the data center 100 serving as VPN gateway for different VPNconnections.

II. Encryption Key Distribution

Some embodiments negotiate different encryption keys for different L4connections (also referred to as flows or transport sessions), and eachhost machines running an applications using one of those L4 connectionswould use the corresponding flow-specific key to perform encryption.Consequently, each host machine only need to perform VPNdecryption/encryption for the L4 connection/session that the hostmachine is running.

FIG. 5 illustrates host machines in a SDDC performing flow-specific VPNencryption and decryption. Specifically, the figure illustrates the SDDC100 having established multiple L4 connections with multiple VPNclients, where different encryption keys encrypt VPN traffic fordifferent flows.

As illustrated, the SDDC 100 has established two L4 connections (orflows) 501 and 502. In some embodiments, each L4 connection isidentifiable by a five-tuple identifier of source IP address,destination IP address, source port, destination port, and transportprotocol. The L4 connection 501 (“conn 1”) is established fortransporting data between an application 511 (“app 1 a”) and anapplication 521 (“app 1 b”). The connection 502 (“conn 2”) isestablished for transporting data between an application 512 (“app 2 a”)and an application 522 (“app 2 b”). The applications 511 is running in aVPN client device 591 and the application 512 is running in a VPN clientdevice 592, while both applications 521 and 522 are running at the hostmachine 114 of the data center 100.

Since both L4 connections 501 and 502 are inter-site connections thatrequire VPN encryption across the Internet, the VPN gateways of eachsite has negotiated keys for each of the L4 connections. Specifically,the VPN traffic of L4 connection 501 uses a key 551 for VPN encryption,while the VPN traffic of L4 connection 502 uses a key 552 for VPNencryption.

As the VPN client device 591 is running an application (the application511) that uses the flow 501, it uses the corresponding key 551 toencrypt/decrypt VPN traffic for the flow 501. Likewise, as the VPNclient device 592 is running an application (the application 512) thatuses the flow 502, it uses the corresponding key 552 to encrypt/decryptVPN traffic for the flow 502. The host machine 114 is runningapplications for both the flows 501 and 502 (i.e., applications 521 and522). It therefore uses both the key 551 and 552 for encrypting anddecrypting VPN traffic (for flows 501 and 502, respectively).

In some embodiments, when multiple different L4 connections areestablished by VPN, the VPN gateway negotiates a key for each of theflows such that the VPN gateway has keys for each of the L4 connections.In some of these embodiments, these keys are then distributed to thehost machines that are running applications that use the correspondingL4 connections. In some embodiments, a host machine obtain the key of aL4 connection from a controller of the datacenter when it query forresolution of destination address (e.g., performing ARP operations fordestination IP address.)

Some embodiments distribute encryption keys to the hosts toencrypt/decrypt the complete payload originating/terminating at thosehosts. In some embodiments, these encryption keys are created orobtained by the VPN gateway based on network security negotiations withthe external networks/devices. In some embodiments, these negotiatedkeys are then distributed to the hosts via control plane of the network.In some embodiments, this creates a complete distributed mesh frameworkfor processing crypto payloads.

In some embodiments, each edge node (i.e., VPN gateway) is responsiblefor both negotiating encryption keys as well as handling packetforwarding. In some embodiments, one set of edge nodes is responsiblefor handling encryption key negotiation, while another set of edge nodesserves as VPN tunnel switch nodes at the perimeter for handling themapping of the outer tunnel tags to the internal network hosts and forforwarding the packets to the correct host for processing, apart fromnegotiating the keys for the connection.

FIGS. 6a-b conceptually illustrate the distribution of VPN encryptionkeys from an edge to host machines through control plane. The figureillustrates a datacenter 600 having several host machines 671-673 aswell as an edge 605 (or multiple edges) that interfaces the Internet andserves as a VPN gateway for the datacenter. The datacenter 600 also hasa controller (or a cluster of controllers) 610 for controlling theoperations of the host machines 671-673 and the edge 605.

The datacenter 600 is also implementing a logical network 620 thatincludes a logical router 621 for performing L3 routing as well aslogical switches 622 and 623 for performing L2 routing. The logicalswitch 622 is for performing L2 switching for a L2 segment that includesVMs 631-633. The logical switch 623 is for performing L2 switching for aL2 segment that includes VMs 634-636. In some embodiments, these logicalentities are implemented in a distributed fashion across host machinesof the datacenter 600. The operations of distributed logical routers andswitches, including ARP operations in a virtual distributed routerenvironment, are described in U.S. patent application Ser. No.14/137,862 filed on Dec. 20, 2013, titled “Logical Router”, published asU.S. Patent Application Publication 2015/0106804. The controller 610controls the host machines of the datacenter 600 in order for those hostmachines to jointly implement the logical entities 621-623.

As illustrated, the datacenter has several on going L4 connections(flows) 641-643 (“Conn 1”, “Conn 2”, and “Conn 3”), and the edge 605 hasnegotiated keys 651-653 for these flows with remote devices or networksexternal to the datacenter 600. The edge 605 negotiates the keys 651-653for these flows. In some embodiments, the edge 605 provides these keysto the controller 610, which serves as a key manager and distributes thekeys 651-653 to the host machines in the datacenter 600. As illustratedin FIG. 6a , the host machines 671-672 are respectively runningapplications for L4 connections (flows) 641-643, and the controllerdistributes corresponding keys 651-653 of those flows to the hostmachines 671-673.

In addition to flow-specific VPN encryption keys, some embodiments alsoprovide keys that are specific to individual L2 segments. In someembodiments, logical switches and logical routers can be global logicalentities (global logical switch and global logical routers) that spanmultiple datacenters. In some embodiments, each global logical switchthat spans multiple datacenter can have a VPN encryption key that isspecific to its VNI (virtual network identifier, VLAN identifier, orVXLAN identifier for identifying a L2 segment). VMs operating indifferent sites but belonging to a same L2 segment (i.e., same globallogical switch and same VNI) can communicate with each other using VPNconnections that are encrypted by a VNI-specific key. As illustrated inFIG. 6b , the logical switch 622 (switch A) has a corresponding VPNencryption key 654 (key A) and the logical switch 623 (switch B) has acorresponding VPN encryption key 655 (key B). These keys are also storedat the edge 605 and can be retrieved by host machines that queries forthem.

As illustrated, the host machine 671 in the datacenter 600 is controlledby the controller 610 through control plane messages. Depending on theapplication that it has to run (on the VMs that it is operating), thehost machine 671 receives from the controller the corresponding VPNencryption keys. As illustrated, the host machine 671 is in VPNconnection with a VPN client device 681 for an application running atits VM 631. Based on this, the host machine 671 queries the key manager610 for the corresponding keys. The key manager 610 in turn provides thekeys 651 and 654.

In some embodiments, the host machine receives encryption keys when itis trying to resolve destination IP addresses during ARP operations. Thecontroller 610 would provide the encryption key to the host machine 671when the queried destination IP is one that requires VPN encryption(i.e., a destination IP that is in another site separated from the localsite). In some embodiments, such a key can be a flow-specific key. Insome embodiments, such a key can be a VNI-specific key. In someembodiments, such a key can be specific to the identity of the VPNclient.

In some embodiments, each key is negotiated for a policy instance 690maintained at the controller 610. These policies in some embodimentsestablishes rules for each flow or for each VNI/L2 segment (e.g., theconditions for rejecting or accepting packets). The controller directsthe edge to negotiate the keys based on these policies for certain flowsor VNIs.

Some embodiments use Distributed Network Encryption (DNE) to establish ashared key for VPN encryption. DNE is a mechanism for distributedentities in a data center to share a key. The key management is donecentrally from an entity called DNE Key Manager, which communicates withDNE Agents in the hypervisors using a secure control channel. The keysare synced between the Agents, which can work then onwards withoutrequiring the DNE Key Manager to be online.

For some embodiments, FIG. 7 conceptually illustrates a process forcreating and using a VPN session. Specifically, the figure illustrates asequence of communications 710-770 between the key manager 610, the VM631, the host 671, the VPN gateway 605, and a VPN client device 681. TheVM 631 is operating in the host machine 671. These communications arefor creating a VPN session between the VM 631 and the VPN client device681, in which the VPN gateway 605 negotiated a key with the clientdevice 681 and the key manager provides the negotiated key to the hostmachine 671.

The communications 710 is for VPN session initiation. The VPN clientdevice 681 initiates a VPN session with the VPN server/gateway 605 viathe server's external IP address. The server gives DNS (domain namesystem) entries to the device. The DNS maps the URLs to the enterpriseIP addresses.

The communications 720 and 725 are for establishing a shared key. Someembodiments uses DNE supports establishment of shared keys among the DNEAgents. The VPN server shares the keys with DNE Manager module in theNSX Manager. The DNE Manager in turns shares the keys among the DNEAgents in the Distributed Switches (DS).

The communications 730 shows a packet from the VPN client device 681 tothe VPN server 605. The VPN stack on the device encrypts andencapsulates the data, which is destined to the VM 631 in the datacenter, and sends the encapsulated payload to the VPN server's externalIP address. The encapsulation is such that the VPN server 605 canauthenticate the payload and find out the VM's IP address.

The communications 740 shows a packet from the VPN server 605 to thehost 671 of VM 631. After the VPN server 605 has authenticated thepayload, it removes the encapsulation. The VPN server 605 reads thedestination IP address and forwards the packet to the VM 631.

The communications 750 shows a packet from the host 671 to theapplication VM 631. The hypervisor in the host 671 gets the packet anduses DNE to decrypt the packet and send the decrypted packet to the VM631.

The communications 760 shows a packet from the VM 631 to the host 671.The L2 packet originating from the VM 631 destined to the VPN clientdevice 681 is forwarded to the hypervisor in the host 671. The DNE inthe hypervisor encrypts the IP datagram and inserts an authenticationheader.

The communications 765 shows a packet from the host 671 to the VPNserver 605. The L2 packet is forwarded to the VPN server's internal IPaddress. This packet may be encapsulated in an overlay protocol such asVXLAN on its way to the VPN server. The VPN server de-capsulate theoverlay if such encapsulation is applied.

The communications 770 shows a packet from the VPN server 605 to the VPNclient device 681. The VPN server 605 encapsulates the L2 payload inanother IP packet and sends it to the device over the public IP network(e.g., Internet). The VPN stack in the VPN client device 681authenticates the packet, removes the encapsulation, decrypts the data,and hands it over to its IP stack.

III. VPN Data Path

As mentioned above, in order to send data packets from its originatingapplication/VM to its destination application/VM through VPN connectionand tunnels, the packet has to go through a series of processingoperations such as encryption, encapsulation, decryption, andde-capsulation. In some embodiments, when a packet is generated by anapplication at a VPN client, the VPN client encrypts the packet with VPNencryption key and processes the packet into an IPSec packet with IPSecheader. The IPSec packet is then sent through the Internet to the VPNgateway of the datacenter, with the content of the packet encrypted. TheVPN gateway of the data center then tunnels the packet to itsdestination tunnel endpoint (a host machine) by encapsulating it (underoverlay such as VXLAN). The host machine that receives the tunnel packetin turn de-capsulate the packet, decrypt the packet, and forward thedecrypted data to the destination VM/application.

In some embodiments, a VPN gateway does not perform VPN encryption ordecryption. When the VPN gateway receives an encrypted VPN packet overthe Internet, it identifies the destination tunnel endpoint (i.e.,destination host machine) and the destination VM without decrypting thepacket. In some embodiments, the VPN gateway uses information in the IPheader to identify destination host machine and destination VM, and theVPN client leaves the IP header unencrypted. In some embodiments, theVPN client encrypt the IP header along with the payload of the packet,but replicates certain portion or fields (e.g., destination IP) of theIP header in an unencrypted portion of the packet so the VPN gatewaywould be able to forward the packet to its destination in the datacenter.

For some embodiment, FIG. 8 illustrates packet-processing operationsthat take place along the VPN connection data path when sending thepacket 170 from the VPN client device 130 to the VM 143 operating in thehost machine 113. The packet 170 originates at the application 120 ofthe VPN client device 130, travels through the edge node 110 of the datacenter 100 to reach the host machine 113 and the VM 143.

The figure illustrates the packet 170 at five sequential stages labeledfrom ‘1’ through ‘5’. At the first stage labeled ‘1’, the App 120produces the packet 170, which includes the application data 872 and IPheader 871. In some embodiments, such header can includes destination IPaddress, source IP addresses, source port, destination port, source MACaddress, and destination MAC address.

At the second stage labeled ‘2’, the VPN client 130 has identified theapplicable VPN encryption key for the packet 170. In some embodiments,this encryption key is the shared key negotiated by the VPN gateway 110with the VPN client 130. The VPN client then encrypts the applicationdata 872 along with the IP header 871. However, since the VPN gateway110 does not perform VPN encryption/decryption at all, the VPN client130 leaves certain fields of the IP header unencrypted. As illustrated,the VPN client 130 stores destination IP 879 in an unencrypted portionof the packet so the VPN gateway 110 would be able to use theunencrypted destination IP field to forward the packet to itsdestination without performing VPN decryption.

At the third stage labeled ‘3’, the VPN client 130 creates a VPNencapsulated packet 172 having a VPN encapsulation header 874 fortransmission across the Internet. In some embodiments, the VPNencapsulation packet 172 is encapsulated according to a tunnelingmechanism over SSL/DTLS or IKE/IPSec. In some embodiments, the VPNencapsulated packet 172 is an IPSec packet and the VPN encapsulationheader is an IPSec Tunnel Mode header. In embodiments, the VPNencapsulated packet comprises a SSL header. In some embodiments, the VPNencapsulation header includes an outer TCP/IP header that identifies theexternal address (or public address) of the VPN gateway 110. The VPNclient 130 then sends the VPN encapsulated packet 172 (with theencrypted IP header 871, the encrypted application data 872, unencrypteddestination IP 879, and the VPN encapsulation header 874) to the VPNgateway 110 of the data center 100.

At the fourth stage labeled ‘4’, the VPN gateway 110 of the data center100 receives the VPN encapsulated packet 172. The VPN gateway 110 inturn uses the unencrypted (or exposed) destination IP 879 to identifydestination host machine and the destination VM of the packet. Nodecryption of the packet is performed at the VPN gateway 110. The VPNgateway 110 then creates an overlay header 875 based on the destinationIP 879. This overlay header is for encapsulating the packet 170 (withencrypted IP header 871 and encrypted application data 872) for anoverlay logical network. In some embodiments, the host machines and theedge gateways of the data center communicates with each other throughoverlay logical networks such as VXLAN, and each host machine andgateway machine is a tunnel endpoint in the overlay logical network (atunnel endpoint in a VXLAN is referred to as VTEP). The VPNencapsulation is removed. The edge then tunnels the encapsulated packetto the destination host machine 113.

At the fifth stage labeled ‘5’, the host machine 113 strips off theoverlay header 875 and decrypt the packet 170 (i.e., the IP header 871and the application data 872) for delivery to the destination VM 143.

For some embodiments, FIG. 9 illustrates the various stages of packetencapsulation and encryption in a distributed tunneling based VPNconnection. The figure illustrates seven different stages 901-907 ofpacket traffic between the App 120 and the VM 143. Each stage shows thestructure the packets traversing along the data path.

The stage 901 shows the structure of a packet 971 produced by the app120 before any encryption and encapsulation. As illustrated, the packetincludes payload 905 and IP header 910, both of which are unencrypted.

The stage 902 shows the structure of the packet 971 after the cryptoengine 160 has encrypted the packet for VPN. As illustrated, the payload905 is encrypted and the crypto engine 160 has added an SSL header 920to the packet. At least a portion of the IP header 910 (e.g.,destination IP address) remains unencrypted.

The stage 903 shows the structure of the packet 971 as its istransmitted by the VPN client 130 for the VPN gateway 110. The packet atthe stage 903 has an outer TCP/IP header 930 that identifies theexternal IP address of the VPN gateway. This external IP address is usedto forward the packet toward the data center across the Internet. Insome embodiments, the outer TCP/IP header is part of a VPN encapsulationheader as described by reference to FIG. 8 above.

The stage 904 shows the structure of the packet 971 that has arrived atthe VPN gateway 110. The VPN gateway has removed the external TCP/IPheader 930 from the packet. The VPN gateway has also created an L2header 940 based on unencrypted IP address 910. The SSL header 920 andthe encrypted payload 905 remain in the packet.

The stage 905 shows the structure of the packet 971 as it isencapsulated by the VPN gateway 110 for transmission over an overlaylogical network (e.g., VXLAN). As illustrated, the packet has overlayencapsulation header 950. The overlay encapsulation header identifiesthe destination host machine 113, which is a tunnel endpoint in theoverlay logical network.

The stage 906 shows the structure of the packet 971 after it has arrivedat the host machine 113. The host machine 113 as tunnel endpoint (VTEP)removes the encapsulation header 950. The SSL header 920 and theencrypted payload 905 remain in the packet along with L2 header 940 andIP address 910.

The stage 907 shows the structure of the packet after the crypto engine165 of the host machine 113 has decrypted it. The crypto engine hasremoved the SSL header 920 as well as decrypted the payload 905. The L2header 940 and the IP header 940 remains in the packet and are used bythe host machine to forward the packet to the VM 143 (through L2 switchand/or L3 router in the hypervisor).

FIG. 10 conceptually illustrates processes 1001 and 1002 for preparing apacket for VPN transmission. Both processes are for sending a packet toa VPN gateway or edge of the data center so the VPN gateway can forwardthe packet to its destination.

In some embodiments, a host machine performs the process 1001 whensending a packet from a VM in a data center to a VPN client. The process1001 starts when it receives (at 1010) a packet from a VM.

The process identifies (at 1015) the destination IP address of thepacket. The process then identifies (at 1020) an encryption key based onthe identified destination IP address. In some embodiments, thisencryption key is negotiated by the VPN gateway and distributed by a keymanager/controller as described in Section II. The process then encrypts(at 1025) the payload of the packet but leaves the destination IPaddress unencrypted or exposed. In some embodiments, the processencrypts the entire IP header of the packet but replicates thedestination IP address in an unencrypted region of the packet.

The process encapsulates (1030) the packet for transmission to the VPNgateway. In some embodiments, the host machine is a tunnel endpoint inan overlay logical network (e.g., VXLAN), and the process encapsulatesthe packet according to the overlay logical network in order to forwardthe packet to the VPN gateway, which is also a tunnel endpoint in theoverlay logical network. In some embodiments, the encapsulationidentifies the internal address (or private address) of the VPN gateway.The process then forwards (at 1035) the encapsulated packet withencrypted payload to the VPN gateway. The process 1001 then ends.

In some embodiments, a VPN client performs the process 1002 when sendinga packet from an app running on the VPN client device to a VM in a datacenter. The process 1002 starts when it receives (at 1050) payload to betransmitted. In some embodiments, the VPN client receives the payloadfrom an application running on the device that needs to communicate witha corresponding application running in the VM in the data center.

The process identifies (at 1055) the destination IP address of thepacket. The process then identifies (at 1060) an encryption key based onthe identified destination IP address. In some embodiments, thisencryption key is negotiated by the VPN gateway and distributed by a keymanager/controller as described in Section II. The process then encrypts(at 1065) the payload of the packet but leaves the destination IPaddress unencrypted or exposed. In some embodiments, the processencrypts the entire IP header of the packet but replicates thedestination IP address in an unencrypted region of the packet.

The process then attaches (at 1070) an outer TCP/IP header to thepacket. This header identifies the outer IP address of the VPN gatewayas its destination. The process then forwards (at 1075) the encryptedpacket toward the VPN gateway (e.g., via the Internet). The process 1002then ends.

FIG. 11 conceptually illustrates a process 1100 for forwarding packet ata VPN gateway of a data center. The process starts when it receives (at1105) a VPN encrypted packet at the VPN server/gateway, which is an edgenode of the data center. In some embodiments, such encryption isaccording to SSL (secure socket layer) or TLS (transport layer security)protocol.

The process then identifies (at 1110) the destination address from anunencrypted portion of the packet. In some embodiments, the VPN gatewaydoes not perform any VPN encryption or decryption (because encryptionand decryption operations are distributed to the host machines hostingthe end machines/VMs). The unencrypted destination address allows theVPN gateway to identify the destination of the packet without having toperform any decryption. In some embodiments, the unencrypted destinationaddress is an IP address, and the entire IP header of the packet isunencrypted. In some embodiments, the IP header of the packet isencrypted, but the addresses that are needed for identification ofdestination (e.g., destination IP) is replicated to an unencryptedportion of the packet.

Next, the process determines (at 1115) whether the VPN encrypted packetis an outgoing packet to a VPN client external to the data center, or anincoming packet to the data center and destined for an applicationrunning in a VM hosted by a host machine. Some embodiments make thisdetermination based on the destination address identified from theunencrypted portion of the packet. If the packet is an incoming packetdestined for a VM operating in the data center, the process proceeds to1120. If the packet is an outgoing packet destined for a VPN clientexternal to the data center, the process proceeds to 1160.

At 1120, the process has determined that the VPN encrypted packet is anincoming packet from an external VPN client. The incoming packet has aVPN encapsulation header (including an outer TCP/IP header) identifyingan external address (or public address) of the VPN gateway. The processremoves the VPN encapsulation header from the packet. The process alsoidentifies (at 1130) the destination endpoint (e.g., VTEP) and the VNI(virtual network identifier) based on the identified destinationaddress. In some embodiments, the VPN gateway has configuration datathat associates address of VMs (L2 MAC address or L3 IP address) withVTEP address of corresponding host machines.

The process then encapsulates (at 1140) the packet according to theidentified VNI and destination endpoint. The process then tunnels (at1150) the encapsulated packet to the identified VTEP, which is also thehost machine that hosts the destination VM. The process 1100 then ends.Once the packet reaches its destination tunnel endpoint, the hostmachine strips the encapsulation, decrypt the VPN encryption, andforward the payload to the VM.

At 1160, the process has determined that the VPN encrypted packet is anoutgoing packet from a host machine of the data center. The outgoingpacket is encapsulated according to an overlay logical network thatallows the packet to be tunneled to the VPN gateway. The process thenremoves the encapsulation. The process also attaches (at 1170) a VPNencapsulation header (including an outer TCP/IP header) based on theidentified destination address from the unencrypted portion of thepacket. The VPN encapsulation header identifies the VPN client for thedestination application. The process then forwards the packet to the VPNclient based on the VPN encapsulation header. The process 1100 thenends. Once the packet reaches the destination VPN client, the VPN clientdevice remove the VPN encapsulation header, decrypts the payload anddelivers the application data.

IV. Partial Decryption at Edge Node

In some embodiments, the edge of a data center stores VPN encryptionkeys that it has negotiated. In order to forward packets to theirrightful destination within a datacenter, the edge in some embodimentsuse the negotiated keys to decrypt at least a portion of each incomingVPN encrypted packet to expose the destination of the encrypted packet.This is necessary for some embodiments in which the identity of thedestination (e.g., its VNI, MAC address, IP address, etc.) is in theencrypted payload of a VPN encrypted packet. In some of theseembodiments, the edge uses information in the header of the VPNencrypted packet to identify the corresponding decryption key and thenuse the identified key to decrypt and reveal the destination informationof the packet.

FIG. 12 illustrates host machines in multi-site environment performingflow-specific VPN encryption and decryption. Specifically, the figureillustrates a multi-site environment having established multiple L4connections across different sites using VPN, where different encryptionkeys encrypt VPN traffic for different flows.

As illustrated, the multi-site environment 200 has established two L4connections (or flows) 1201 and 1202. In some embodiments, each L4connection is identifiable by a five-tuple identifier of source IPaddress, destination IP address, source port, destination port, andtransport protocol. The L4 connection 1201 (“conn 1”) is established fortransporting data between an application 1211 (“app 1 a”) and anapplication 1221 (“app 1 b”). The connection 1202 (“conn 2”) isestablished for transporting data between an application 1212 (“app 2a”) and an application 1222 (“app 2 b”). The applications 1211 isrunning in the host machine 212 and the application 1212 is running inthe host machine 213, while both applications 1221 and 1222 are runningin site B at the host machine 223.

Since both L4 connections 1201 and 1202 are inter-site connections thatrequire VPN encryption across the Internet, the VPN gateways of eachsite has negotiated keys for each of the L4 connections. Specifically,the VPN traffic of L4 connection 1201 uses a key 1251 for VPNencryption, while the VPN traffic of L4 connection 1202 uses a key 1252for VPN encryption.

As the host machine 212 is running an application (the application 1211)that uses the flow 1201, it uses the corresponding key 1251 toencrypt/decrypt VPN traffic for the flow 1201. Likewise, as the hostmachine 213 is running an application (the application 1212) that usesthe flow 1202, it uses the corresponding key 1252 to encrypt/decrypt VPNtraffic for the flow 1202. The host machine 223 is running applicationsfor both the flows 1201 and 1202 (i.e., applications 1221 and 1222). Ittherefore uses both the key 1251 and 1252 for encrypting and decryptingVPN traffic (for flows 1201 and 1202, respectively).

As mentioned, VPN encryption keys are generated based on the negotiationbetween the VPN gateways (i.e., edge nodes of datacenters/sites). Insome embodiments, when multiple different L4 connections are establishedby VPN, the VPN gateway negotiates a key for each of the flows such thatthe VPN gateway has keys for each of the L4 connections. In some ofthese embodiments, these keys are then distributed to the host machinesthat are running applications that use the corresponding L4 connections.In some embodiments, a host machine obtain the key of a L4 connectionfrom a controller of the datacenter when it query for resolution ofdestination address (e.g., performing ARP operations for destination IPaddress.) In some embodiments, a VPN gateway that negotiated a key alsokeeps a copy of the key for subsequent partial decryption of packets foridentifying the destination of the packet within the data center.

FIG. 13 conceptually illustrate the distribution of VPN encryption keysfrom an edge to host machines through control plane. The figureillustrates a datacenter 1300 having several host machines 1371-1373 aswell as an edge 1305 (or multiple edges) that interfaces the Internetand serves as a VPN gateway for the datacenter. The datacenter 1300 alsohas a controller (or a cluster of controllers) 1310 for controlling theoperations of the host machines 1371-1373 and the edge 1305.

The datacenter 1300 is also implementing a logical network 1320 thatincludes a logical router 1321 for performing L3 routing as well aslogical switches 1322 and 1323 for performing L2 routing. The logicalswitch 1322 is for performing L2 switching for a L2 segment thatincludes VMs 1331-1333. The logical switch 1323 is for performing L2switching for a L2 segment that includes VMs 1334-1336. In someembodiments, these logical entities are implemented in a distributedfashion across host machines of the datacenter 1300. The controller 1310controls the host machines of the datacenter 1300 in order for thosehost machines to jointly implement the logical entities 1321-1323.

As illustrated, the datacenter has several on going L4 connections(flows) 1341-1343 (“Conn 1”, “Conn 2”, and “Conn 3”), and the edge 1305has negotiated keys 1351-1353 for these flows with remote devices ornetworks external to the datacenter 1300. The edge 1305 negotiates thekeys 1351-1353 for these flows and stores the negotiated keys 1351-1353at the edge 1305. In some embodiments, these keys are distributed tothose host machines by the controller 1310. As illustrated in FIG. 13,the host machines 1371-1372 are respectively running applications for L4connections (flows) 1341-1343, and the controller distributescorresponding keys 1351-1353 of those flows to the host machines1371-1373.

For some embodiments, FIG. 14 conceptually illustrates a process 1400that is performed by a host machine in a datacenter that uses VPN tocommunicate with external network or devices. The process 1400 startswhen it receives (at 1410) an outgoing packet to be forwarded from anapplication running on a VM.

The process then identifies (at 1420) the destination IP address of theoutgoing packet and determines (at 1430) whether the destination IPaddress need to be resolved, i.e., whether the next hop based on thedestination IP address is known. In some embodiments, the next hop isidentified by its VNI and MAC address. In some embodiments, the next hopis behind a virtual tunnel and the packet is to be forwarded accordingto a tunnel endpoint address (VTEP), which can corresponds to anotherhost machine or physical router in the network. If the next hop addressis already resolved, the process proceeds to 1440. If the next hopaddress is not resolved, the process proceeds to 1435.

At 1435, the process performs ARP in order to receive the necessaryaddress resolution information from the controller. Such information insome embodiments includes the VNI, the MAC address, and/or the VTEP ofnext hop. In some embodiments, such information also includes VPNencryption key if the data is to be transmitted via a VPN connection. Insome embodiments, such information includes a remote network's topologyusing host tags so that the secure overlay traffic travels directly tohost machines in the remote networks where the workload is located. Theprocess then proceeds to 1440.

At 1440, the process determines if VPN encryption is necessary for thenext hop. Some embodiments make this determination based on the earlierARP response from 1435, which informs the process whether packet has tobe encrypted for VPN and provides a corresponding key if encryption isnecessary. Some embodiments make this determination based on securitypolicy or rules applicable to the packet. If the VPN encryption isnecessary, the process proceeds to 1445. Otherwise the process proceedsto 1450.

At 1445, the process identifies the applicable VPN encryption key andencrypts the packet. In some embodiments, the host machine may operatemultiple VMs having applications requiring different encryption keys(e.g., for packets belonging to different flows or different L2segments.) The process would thus use information in packet (e.g., L4flow identifier or L2 segment identifier) to identify the correctcorresponding key. The process then proceeds to 1450.

At 1450, the process encapsulates the (encrypted) packet according tothe resolved next hop information (i.e., the destination VTEP, MACaddress, and VNI) so the packet can be tunneled to its destination. Theprocess then forwards (at 1460) the encapsulated packet to itsdestination, i.e., to the edge so the edge can forward the packet to theexternal device through the Internet. After forwarding the encapsulatedpacket, the process 1400 ends.

As mentioned above by reference to FIGS. 1 and 2, in order to send datapackets from its originating application/VM to its destinationapplication/VM through VPN connection and tunnels, the packet has to gothrough a series of processing operations such as encryption,encapsulation, decryption, and de-capsulation. In some embodiments, whena packet is generated by an application at a particular datacenter orsite, the host machine running the application encrypts the packet withVPN encryption key and then encapsulates the packet (using overlay suchas VXLAN) in order to tunnel the to the edge. The edge in turn processesthe packet into an IPSec packet with IPSec header. The IPSec packet isthen sent through the Internet to another datacenter or site, with thecontent of the packet encrypted. The edge of the other site then tunnelsthe packet to its destination tunnel endpoint (a host machine) byencapsulating it (under overlay such as VXLAN). The host machine thatreceives the tunnel packet in turn de-capsulate the packet, decrypt thepacket, and forward the decrypted data to the destinationVM/application. In some embodiments, the edge of the other site uses itsstored negotiated keys to decrypt a portion of the packet in order toidentify the destination tunnel endpoint in that other site.

For some embodiment, FIG. 15 illustrates packet-processing operationsthat take place along the data path when sending a packet 1570 from onesite (the site 201) to another site (the site 202) by using VPN. Thepacket 1570 originates at the VM 231 of the host machine 212, travelsthrough the edge node 210 of site 201 and the edge node 220 of the site202 to reach the host machine 223 and the VM 232.

The figure illustrates the packet 1570 at five sequential stages labeledfrom ‘1’ through ‘5’. At the first stage labeled ‘1’, the VM 231produces the packet 1570, which includes the application data 1571 andIP header data 1572. In some embodiments, such header can includesdestination IP address, source IP addresses, source port, destinationport, source MAC address, and destination MAC address. The packet 1570is not encrypted at operation ‘1’. In some embodiments, the informationin the IP header refers to topologies of the source datacenter (i.e.,the site 201) that the security policy of the datacenter may not want toreveal, and hence the subsequent VPN encryption operations will encryptthe IP header as well as the application data.

At the second stage labeled ‘2’, the host machine 212 has identified theapplicable VPN encryption key for the packet 1500 based on the contentof the IP header 1571 (e.g., by identifying the flow/L4 connection or byidentifying the VNI/L2 segment). The host machine then encrypted the IPheader 1571 and well as the application data 1572 (shown in hash).Furthermore, based on the information of the IP header 1571, the hostmachine has encapsulated the packet 1570 for an overlay logical network(e.g., VXLAN) with an overlay header 1573 in order to tunnel the packetto the edge 210 of site 201.

At the third stage labeled ‘3’, the edge 210 receives the tunneledpacket and strips off the overlay header 1573. The edge then creates anIPSec packet for transmission across the Internet. The IPSec packetincludes an IPSec Tunnel Mode header 1574 that is based on theinformation in the stripped off overlay header 1573. This IPSec header1574 includes information that can be used to identify the VPNencryption key (e.g., in the SPI field of the IPSec header). The edge210 then sends packet 1570 (with the encrypted IP header 1571, theencrypted application data 1572, and their corresponding IPSec TunnelMode header 1573) toward the edge 220 of the site 202.

At the fourth stage labeled ‘4’, the edge 220 of the site 202 uses theinformation in the IPSec Tunnel Mode header to 1573 to identify the keyused for the encryption and decrypt enough of the IP header 1571 inorder to create an overlay header 1575. This overlay header is forencapsulating the packet 1570 (with encrypted IP header 1571 andencrypted application data 1572) for an overlay logical network (e.g.,VXLAN). The edge then tunnels the encapsulated packet to the hostmachine 223.

At the fifth stage labeled ‘5’, the host machine 223 strips off theoverlay header 1575 and decrypt the packet 1570 (i.e., the IP header1571 and the application data 1572) for delivery to the destination VM232.

As mentioned, the encryption keys used by the host machines to encryptand decrypt VPN traffic are edge-negotiated keys. The edge as VPNgateway negotiates these keys according to security policies of thetenant or the logical network that is using the VPN connection, specificto a L4 connection or a L2 segment (logical switch). The controller thendistributes negotiated keys to the host machines so the host machineperforms the actual encryption and decryption. The edge is in turntasked with forwarding the incoming encrypted VPN traffic to theirrightful destinations.

However, in order to forward packets to their rightful destinationwithin a datacenter, the edge in some embodiments nevertheless has touse the negotiated keys to decrypt at least a portion of each incomingVPN encrypted packet in order to reveal the destination of the encryptedpacket. This is necessary for some embodiments in which the identity ofthe destination (e.g., its VNI, MAC address, IP address, etc.) is inencrypted payload of a VPN encrypted packet. In some of theseembodiments, the edge uses information in the header of the VPNencrypted packet to identify the corresponding decryption key and thenuse the identified key to decrypt and reveal the destination informationof the packet.

FIG. 16 illustrates using partial decryption of the VPN encrypted packetto identify the packet's rightful destination. The figure illustratesthe forwarding of a VPN encrypted packet 1670 by the edge 220 of thedatacenter 202. The received VPN encrypted packet 1670 is an IPSecpacket arriving at the edge 220 from the Internet from anotherdatacenter. As the packet 1670 arrives at the edge 220, it has anencrypted payload 1671 and an unencrypted IPSec header 1672. The payload1671 includes both IP header 1673 and application data 1683.

Since the header 1672 of the IPSec is an IPSec tunnel mode header thatis not encrypted, it can be read directly by the edge 220. The IPSectunnel mode header 1672 includes field that identifies the flow or L4connection that the packet 1670 belongs to. In some embodiments in whichthe VPN encrypted packet is an IPSec packet, the SPI field of the IPSecheader provides the identity of the flow. The edge 220 in turn uses theidentity of the flow provided by the IPSec header to select/identify acorresponding encryption key 252.

The edge 220 in turn uses the identified key 252 to decrypt a portion ofthe encrypted payload 1671 of the packet 1670, revealing the first fewbytes (e.g., the header portion) 1673 of the payload. In someembodiment, the edge 220 would halt the decryption operation once thesefirst few bytes are revealed in some embodiments. Based on the revealedbytes, the edge determines the identity of the destination andencapsulates the encrypted payload 1671 into an encapsulated packet 1674by adding an overlay header 1676. In some embodiments, thisencapsulation is for tunneling in overlay logical network such as VXLAN.The encapsulated packet 1674 is tunneled to the destination host machine222.

Once the encapsulated packet 1674 reaches the host machine 222, the hostmachine uses the VPN encryption key 252 to decrypt the encrypted payload1671. If the host machine 222 does not have the key, it would perform anARP like operation and queries the controller for the key based oneither the VNI or the destination IP. The decryption results in adecrypted payload 1675, which is provided to the destination VM 262.

For some embodiments, FIG. 17 conceptually illustrates a process 1700for forwarding VPN encrypted packet at an edge node. In someembodiments, the process 1700 is performed by an edge of the datacentersuch as the edge node 220.

The process 1700 starts when it receives (at 1710) a packet from outsideof the network/datacenter. In some embodiments, the payload of thispacket is encrypted based on a VPN encryption key. In some embodiments,the packet is an IPSec packet.

Next, the process identifies (1720) a VPN encryption key based on theheader data of the packet. In some embodiments in which the packet is anIPSec packet, the header of the IPSec packet is not encrypted. Such apacket header in some embodiments includes information that can be usedto identify VPN encryption key. In some embodiments, these indicationincludes the flow/L4 connection of the IPSec packet. Consequently, theprocess is able to identify the encryption key based on the indicationprovided by the header by e.g., using the flow identifier of the IPSecpacket to identify the corresponding VPN encryption key.

The process then uses (1730) the identified key to decrypt the startingbytes of the encrypted payload in order to reveal these bytes to theedge node. In some embodiments, the starting bytes of the encryptedpayload include information that can be used to determine the next hopafter the edge node, information such as destination IP address,destination VNI, destination VTEP, destination MAC address, etc. Theprocess then uses the decrypted bytes to identify (at 1740) the next hopinformation. In some embodiments, the process performs L3 routingoperations based on the information in the revealed bytes (e.g.,destination IP address) in order to identify the destination VNI,destination VTEP, or next hop MAC.

Next, the process encapsulates (1750) packets based on the identifiedVNI. In some embodiments, the encrypted payload of the IPSec isencapsulated under VXLAN format based on the earlier identifiedinformation (e.g., destination VNI and VTEP).

The process then forwards (1760) the encapsulated packet to theidentified destination (e.g., a host machine as the VTEP). The process1700 then ends.

V. Computing Device and Virtualization Software

FIG. 18 illustrates a computing device 1800 that serves as a hostmachine or edge gateway (i.e., VPN gateway or VPN server) for someembodiments of the invention. The computing device 1800 is runningvirtualization software that implements a physical switching element anda set of physical routing elements. (i.e., MPSE and MPREs).

As illustrated, the computing device 1800 has access to a physicalnetwork 1890 through a physical NIC (PNIC) 1895. The host machine 1800also runs the virtualization software 1805 and hosts VMs 1811-1814. Thevirtualization software 1805 serves as the interface between the hostedVMs and the physical NIC 1895 (as well as other physical resources, suchas processors and memory). Each of the VMs includes a virtual NIC (VNIC)for accessing the network through the virtualization software 1805. EachVNIC in a VM is responsible for exchanging packets between the VM andthe virtualization software 1805. In some embodiments, the VNICs aresoftware abstractions of physical NICs implemented by virtual NICemulators.

The virtualization software 1805 manages the operations of the VMs1811-1814, and includes several components for managing the access ofthe VMs to the physical network (by implementing the logical networks towhich the VMs connect, in some embodiments). As illustrated, thevirtualization software includes several components, including a MPSE1820, a set of MPREs 1830, a controller agent 1840, a VTEP 1850, acrypto engine 1875, and a set of uplink pipelines 1870.

The VTEP (VXLAN tunnel endpoint) 1850 allows the host machine 1800 toserve as a tunnel endpoint for logical network traffic (e.g., VXLANtraffic). VXLAN is an overlay network encapsulation protocol. An overlaynetwork created by VXLAN encapsulation is sometimes referred to as aVXLAN network, or simply VXLAN. When a VM on the host 1800 sends a datapacket (e.g., an ethernet frame) to another VM in the same VXLAN networkbut on a different host, the VTEP will encapsulate the data packet usingthe VXLAN network's VNI and network addresses of the VTEP, beforesending the packet to the physical network. The packet is tunneledthrough the physical network (i.e., the encapsulation renders theunderlying packet transparent to the intervening network elements) tothe destination host. The VTEP at the destination host decapsulates thepacket and forwards only the original inner data packet to thedestination VM. In some embodiments, the VTEP module serves only as acontroller interface for VXLAN encapsulation, while the encapsulationand decapsulation of VXLAN packets is accomplished at the uplink module1870.

The controller agent 1840 receives control plane messages from acontroller or a cluster of controllers. In some embodiments, thesecontrol plane message includes configuration data for configuring thevarious components of the virtualization software (such as the MPSE 1820and the MPREs 1830) and/or the virtual machines. In the exampleillustrated in FIG. 18, the controller agent 1840 receives control planemessages from the controller cluster 1860 from the physical network 1890and in turn provides the received configuration data to the MPREs 1830through a control channel without going through the MPSE 1820. However,in some embodiments, the controller agent 1840 receives control planemessages from a direct data conduit (not illustrated) independent of thephysical network 1890. In some other embodiments, the controller agentreceives control plane messages from the MPSE 1820 and forwardsconfiguration data to the router 1830 through the MPSE 1820. In someembodiments, the controller agent 1840 also serve as the DNE agent ofthe host machine, responsible for receiving VPN encryption keys from akey manager (which can be the controller). Distribution of encryptionkeys under DNE is described by reference to FIG. 14 above.

The MPSE 1820 delivers network data to and from the physical NIC 1895,which interfaces the physical network 1890. The MPSE also includes anumber of virtual ports (vPorts) that communicatively interconnects thephysical NIC with the VMs 1811-1814, the MPREs 1830 and the controlleragent 1840. Each virtual port is associated with a unique L2 MACaddress, in some embodiments. The MPSE performs L2 link layer packetforwarding between any two network elements that are connected to itsvirtual ports. The MPSE also performs L2 link layer packet forwardingbetween any network element connected to any one of its virtual portsand a reachable L2 network element on the physical network 1890 (e.g.,another VM running on another host). In some embodiments, a MPSE is alocal instantiation of a logical switching element (LSE) that operatesacross the different host machines and can perform L2 packet switchingbetween VMs on a same host machine or on different host machines. Insome embodiments, the MPSE performs the switching function of severalLSEs according to the configuration of those logical switches.

The MPREs 1830 perform L3 routing on data packets received from avirtual port on the MPSE 1820. In some embodiments, this routingoperation entails resolving L3 IP address to a next-hop L2 MAC addressand a next-hop VNI (i.e., the VNI of the next-hop's L2 segment). Eachrouted data packet is then sent back to the MPSE 1820 to be forwarded toits destination according to the resolved L2 MAC address. Thisdestination can be another VM connected to a virtual port on the MPSE1820, or a reachable L2 network element on the physical network 1890(e.g., another VM running on another host, a physical non-virtualizedmachine, etc.).

As mentioned, in some embodiments, a MPRE is a local instantiation of alogical routing element (LRE) that operates across the different hostmachines and can perform L3 packet forwarding between VMs on a same hostmachine or on different host machines. In some embodiments, a hostmachine may have multiple MPREs connected to a single MPSE, where eachMPRE in the host machine implements a different LRE. MPREs and MPSEs arereferred to as “physical” routing/switching element in order todistinguish from “logical” routing/switching elements, even though MPREsand MPSE are implemented in software in some embodiments. In someembodiments, a MPRE is referred to as a “software router” and a MPSE isreferred to a “software switch”. In some embodiments, LREs and LSEs arecollectively referred to as logical forwarding elements (LFEs), whileMPREs and MPSEs are collectively referred to as managed physicalforwarding elements (MPFEs).

In some embodiments, the MPRE 1830 includes one or more logicalinterfaces (LIFs) that each serves as an interface to a particularsegment (L2 segment or VXLAN) of the network. In some embodiments, eachLIF is addressable by its own IP address and serve as a default gatewayor ARP proxy for network nodes (e.g., VMs) of its particular segment ofthe network. In some embodiments, all of the MPREs in the different hostmachines are addressable by a same “virtual” MAC address (or vMAC),while each MPRE is also assigned a “physical” MAC address (or pMAC) inorder indicate in which host machine does the MPRE operate.

The crypto engine 1875 applies encryption key to decrypt incoming datafrom the physical network and to encrypt outgoing data to the physicalnetwork 1890. In some embodiments, a controller sends the encryption keyto the virtualization software 1805 through control plane messages, andthe crypto engine 1875 identifies a corresponding key from among thereceived keys for decrypting incoming packets and for encryptingoutgoing packets. In some embodiments, the controller agent 1840receives the control plane messages, and the keys delivered by thecontrol plane messages is stored in a key store 1878 that can beaccessed by the crypto engine 1875.

The uplink module 1870 relays data between the MPSE 1820 and thephysical NIC 1895. The uplink module 1870 includes an egress chain andan ingress chain that each performs a number of operations. Some ofthese operations are pre-processing and/or post-processing operationsfor the MPRE 1830. The operations of LIFs, uplink module, MPSE, and MPREare described in U.S. patent application Ser. No. 14/137,862 filed onDec. 20, 2013, titled “Logical Router”, published as U.S. PatentApplication Publication 2015/0106804.

As illustrated by FIG. 18, the virtualization software 1805 has multipleMPREs for multiple different LREs. In a multi-tenancy environment, ahost machine can operate virtual machines from multiple different usersor tenants (i.e., connected to different logical networks). In someembodiments, each user or tenant has a corresponding MPRE instantiationof its LRE in the host for handling its L3 routing. In some embodiments,though the different MPREs belong to different tenants, they all share asame vPort on the MPSE 1820, and hence a same L2 MAC address (vMAC orpMAC). In some other embodiments, each different MPRE belonging to adifferent tenant has its own port to the MPSE.

The MPSE 1820 and the MPRE 1830 make it possible for data packets to beforwarded amongst VMs 1811-1814 without being sent through the externalphysical network 1890 (so long as the VMs connect to the same logicalnetwork, as different tenants' VMs will be isolated from each other).Specifically, the MPSE performs the functions of the local logicalswitches by using the VNIs of the various L2 segments (i.e., theircorresponding L2 logical switches) of the various logical networks.Likewise, the MPREs perform the function of the logical routers by usingthe VNIs of those various L2 segments. Since each L2 segment/L2 switchhas its own a unique VNI, the host machine 1800 (and its virtualizationsoftware 1805) is able to direct packets of different logical networksto their correct destinations and effectively segregates traffic ofdifferent logical networks from each other.

VI. Electronic Device

Many of the above-described features and applications are implemented assoftware processes that are specified as a set of instructions recordedon a computer readable storage medium (also referred to as computerreadable medium). When these instructions are executed by one or moreprocessing unit(s) (e.g., one or more processors, cores of processors,or other processing units), they cause the processing unit(s) to performthe actions indicated in the instructions. Examples of computer readablemedia include, but are not limited to, CD-ROMs, flash drives, RAM chips,hard drives, EPROMs, etc. The computer readable media does not includecarrier waves and electronic signals passing wirelessly or over wiredconnections.

In this specification, the term “software” is meant to include firmwareresiding in read-only memory or applications stored in magnetic storage,which can be read into memory for processing by a processor. Also, insome embodiments, multiple software inventions can be implemented assub-parts of a larger program while remaining distinct softwareinventions. In some embodiments, multiple software inventions can alsobe implemented as separate programs. Finally, any combination ofseparate programs that together implement a software invention describedhere is within the scope of the invention. In some embodiments, thesoftware programs, when installed to operate on one or more electronicsystems, define one or more specific machine implementations thatexecute and perform the operations of the software programs.

FIG. 19 conceptually illustrates an electronic system 1900 with whichsome embodiments of the invention are implemented. The electronic system1900 can be used to execute any of the control, virtualization, oroperating system applications described above. The electronic system1900 may be a computer (e.g., a desktop computer, personal computer,tablet computer, server computer, mainframe, a blade computer etc.),phone, PDA, or any other sort of electronic device. Such an electronicsystem includes various types of computer readable media and interfacesfor various other types of computer readable media. Electronic system1900 includes a bus 1905, processing unit(s) 1910, a system memory 1925,a read-only memory 1930, a permanent storage device 1935, input devices1940, and output devices 1945.

The bus 1905 collectively represents all system, peripheral, and chipsetbuses that communicatively connect the numerous internal devices of theelectronic system 1900. For instance, the bus 1905 communicativelyconnects the processing unit(s) 1910 with the read-only memory 1930, thesystem memory 1925, and the permanent storage device 1935.

From these various memory units, the processing unit(s) 1910 retrievesinstructions to execute and data to process in order to execute theprocesses of the invention. The processing unit(s) may be a singleprocessor or a multi-core processor in different embodiments.

The read-only-memory (ROM) 1930 stores static data and instructions thatare needed by the processing unit(s) 1910 and other modules of theelectronic system. The permanent storage device 1935, on the other hand,is a read-and-write memory device. This device is a non-volatile memoryunit that stores instructions and data even when the electronic system1900 is off. Some embodiments of the invention use a mass-storage device(such as a magnetic or optical disk and its corresponding disk drive) asthe permanent storage device 1935.

Other embodiments use a removable storage device (such as a floppy disk,flash drive, etc.) as the permanent storage device. Like the permanentstorage device 1935, the system memory 1925 is a read-and-write memorydevice. However, unlike storage device 1935, the system memory is avolatile read-and-write memory, such a random access memory. The systemmemory stores some of the instructions and data that the processor needsat runtime. In some embodiments, the invention's processes are stored inthe system memory 1925, the permanent storage device 1935, and/or theread-only memory 1930. From these various memory units, the processingunit(s) 1910 retrieves instructions to execute and data to process inorder to execute the processes of some embodiments.

The bus 1905 also connects to the input and output devices 1940 and1945. The input devices enable the user to communicate information andselect commands to the electronic system. The input devices 1940 includealphanumeric keyboards and pointing devices (also called “cursor controldevices”). The output devices 1945 display images generated by theelectronic system. The output devices include printers and displaydevices, such as cathode ray tubes (CRT) or liquid crystal displays(LCD). Some embodiments include devices such as a touchscreen thatfunction as both input and output devices.

Finally, as shown in FIG. 19, bus 1905 also couples electronic system1900 to a network 1965 through a network adapter (not shown). In thismanner, the computer can be a part of a network of computers (such as alocal area network (“LAN”), a wide area network (“WAN”), or an Intranet,or a network of networks, such as the Internet. Any or all components ofelectronic system 1900 may be used in conjunction with the invention.

Some embodiments include electronic components, such as microprocessors,storage and memory that store computer program instructions in amachine-readable or computer-readable medium (alternatively referred toas computer-readable storage media, machine-readable media, ormachine-readable storage media). Some examples of such computer-readablemedia include RAM, ROM, read-only compact discs (CD-ROM), recordablecompact discs (CD-R), rewritable compact discs (CD-RW), read-onlydigital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a varietyof recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD-RW, etc.),flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.),magnetic and/or solid state hard drives, read-only and recordableBlu-Ray® discs, ultra density optical discs, any other optical ormagnetic media, and floppy disks. The computer-readable media may storea computer program that is executable by at least one processing unitand includes sets of instructions for performing various operations.Examples of computer programs or computer code include machine code,such as is produced by a compiler, and files including higher-level codethat are executed by a computer, an electronic component, or amicroprocessor using an interpreter.

While the above discussion primarily refers to microprocessor ormulti-core processors that execute software, some embodiments areperformed by one or more integrated circuits, such as applicationspecific integrated circuits (ASICs) or field programmable gate arrays(FPGAs). In some embodiments, such integrated circuits executeinstructions that are stored on the circuit itself.

As used in this specification, the terms “computer”, “server”,“processor”, and “memory” all refer to electronic or other technologicaldevices. These terms exclude people or groups of people. For thepurposes of the specification, the terms display or displaying meansdisplaying on an electronic device. As used in this specification, theterms “computer readable medium,” “computer readable media,” and“machine readable medium” are entirely restricted to tangible, physicalobjects that store information in a form that is readable by a computer.These terms exclude any wireless signals, wired download signals, andany other ephemeral signals.

In this document, the term “packet” refers to a collection of bits in aparticular format sent across a network. One of ordinary skill in theart will recognize that the term packet may be used herein to refer tovarious formatted collections of bits that may be sent across a network,such as Ethernet frames, TCP segments, UDP datagrams, IP packets, etc.

This specification refers throughout to computational and networkenvironments that include virtual machines (VMs). However, virtualmachines are merely one example of data compute nodes (DCNs) or datacompute end nodes, also referred to as addressable nodes. DCNs mayinclude non-virtualized physical hosts, virtual machines, containersthat run on top of a host operating system without the need for ahypervisor or separate operating system, and hypervisor kernel networkinterface modules.

VMs, in some embodiments, operate with their own guest operating systemson a host using resources of the host virtualized by virtualizationsoftware (e.g., a hypervisor, virtual machine monitor, etc.). The tenant(i.e., the owner of the VM) can choose which applications to operate ontop of the guest operating system. Some containers, on the other hand,are constructs that run on top of a host operating system without theneed for a hypervisor or separate guest operating system. In someembodiments, the host operating system uses name spaces to isolate thecontainers from each other and therefore provides operating-system levelsegregation of the different groups of applications that operate withindifferent containers. This segregation is akin to the VM segregationthat is offered in hypervisor-virtualized environments that virtualizesystem hardware, and thus can be viewed as a form of virtualization thatisolates different groups of applications that operate in differentcontainers. Such containers are more lightweight than VMs.

Hypervisor kernel network interface modules, in some embodiments, is anon-VM DCN that includes a network stack with a hypervisor kernelnetwork interface and receive/transmit threads. One example of ahypervisor kernel network interface module is the vmknic module that ispart of the ESXi™ hypervisor of VMware, Inc.

One of ordinary skill in the art will recognize that while thespecification refers to VMs, the examples given could be any type ofDCNs, including physical hosts, VMs, non-VM containers, and hypervisorkernel network interface modules. In fact, the example networks couldinclude combinations of different types of DCNs in some embodiments.

While the invention has been described with reference to numerousspecific details, one of ordinary skill in the art will recognize thatthe invention can be embodied in other specific forms without departingfrom the spirit of the invention. In addition, a number of the figures(including FIGS. 10, 11, and 14) conceptually illustrate processes. Thespecific operations of these processes may not be performed in the exactorder shown and described. The specific operations may not be performedin one continuous series of operations, and different specificoperations may be performed in different embodiments. Furthermore, theprocess could be implemented using several sub-processes, or as part ofa larger macro process. Thus, one of ordinary skill in the art wouldunderstand that the invention is not to be limited by the foregoingillustrative details, but rather is to be defined by the appendedclaims.

What is claimed is:
 1. For facilitating virtual private network (VPN)connections, a method for forwarding a packet from a logical networkthat is defined over a physical network of a datacenter to a VPN clientoutside of the datacenter through a particular VPN connection between ahost computer inside of the datacenter and the VPN client outside of thedatacenter, the method comprising: receiving, at a computing device inthe datacenter, a packet comprising an encapsulating first outer headerand a payload, the encapsulating first outer header storing a logicalnetwork identifier that identifies the logical network to which thepacket is associated, and the payload of the packet comprising anunencrypted portion and an encrypted portion that was encrypted by thehost computer for the particular VPN connection with the VPN client;identifying, from said unencrypted portion of the encapsulated payload,a network address of the VPN client outside of the datacenter as adestination of the received packet; replacing the encapsulating firstouter header of the packet with an encapsulating second outer VPN headerfor the particular VPN connection, the second outer VPN headerspecifying the identified network address of the VPN client as thedestination address of the packet; and forwarding the packet with theencapsulating second outer VPN header to the VPN client outside of thedatacenter, wherein the VPN client decapsulates the packet and decryptsthe encrypted portion of the payload of the packet.
 2. The method ofclaim 1, wherein said computing device is an edge node of the datacenterthat comprises a plurality of host computers executing machinesconnected to the logical network.
 3. The method of claim 2, wherein thereceived encapsulated packet is tunneled to the computing device fromthe host computer, wherein the host computer and the computing deviceare tunnel endpoints of an overlay logical network.
 4. The method ofclaim 3, wherein the computing device is a VPN gateway that negotiatedwith the VPN client for an encryption key that is used to encrypt theencrypted portion of the packet, wherein the encryption key is providedto the host computer for encrypting the packet.
 5. The method of claim1, wherein the encapsulating first outer header is a header added to thepacket when the packet is sent by a machine executing on the hostcomputer in order to produce the received encapsulated packet, thepacket further comprising a first header storing network addressesdefined for the logical network, said encapsulating first outer headerallowing the packet to traverse through the physical network of thedatacenter while preserving network addresses defined for the logicalnetwork.
 6. A non-transitory machine readable medium storing a programfor facilitating virtual private network (VPN) connections by forwardinga packet from a logical network that is defined over a physical networkof a datacenter to a VPN client outside of the datacenter through aparticular VPN connection between a host computer inside of thedatacenter and the VPN client outside of the datacenter, the program forexecution by at least one processing unit of a computing device, theprogram comprising sets of instructions for: receiving, at a computingdevice in the datacenter, a packet comprising an encapsulating firstouter header and a payload, the encapsulating first outer header storinga logical network identifier that identifies the logical network towhich the packet is associated, and the payload of the packet comprisingan unencrypted portion and an encrypted portion that was encrypted bythe host computer for the particular VPN connection with the VPN client;identifying, from said unencrypted portion of the encapsulated payload,a network address of the VPN client outside of the datacenter as adestination of the received packet; replacing the encapsulating firstouter header of the packet with an encapsulating second outer VPN headerfor the particular VPN connection, the second outer VPN headerspecifying the identified network address of the VPN client as thedestination address of the packet; and forwarding the packet with theencapsulating second outer VPN header to the VPN client outside of thedatacenter, wherein the VPN client decapsulates the packet and decryptsthe encrypted portion of the payload of the packet.
 7. Thenon-transitory machine readable medium of claim 6, wherein saidcomputing device is an edge node of the datacenter that comprises aplurality of host computers executing machines connected to the logicalnetwork.
 8. The non-transitory machine readable medium of claim 7,wherein the received encapsulated packet is tunneled to the computingdevice from the host computer, wherein the host computer and thecomputing device are tunnel endpoints of an overlay logical network. 9.The non-transitory machine readable medium of claim 8, wherein thecomputing device is a VPN gateway that negotiated with the VPN clientfor an encryption key that is used to encrypt the encrypted portion ofthe packet, wherein the encryption key is provided to the host computerfor encrypting the packet.
 10. The non-transitory machine readablemedium of claim 6, wherein the encapsulating first outer header is aheader added to the packet when the packet is sent by a machineexecuting on the host computer in order to produce the receivedencapsulated packet, the packet further comprising a first headerstoring network addresses defined for the logical network, saidencapsulating first outer header allowing the packet to traverse throughthe physical network of the datacenter while preserving networkaddresses defined for the logical network.